APPARATUS, METHOD AND COVERING DIE FOR PRODUCING A LONG FIBER-REINFORCED THERMOPLASTIC COMPOSITION

Abstract: An apparatus, a method and a covering die for producing a long fiber-reinforced thermoplastic composition for reducing unevenness in extrusion in a web width direction when covering a bundle of continuous fibers which are opened in a web form with fused thermoplastic resin extruded from a slit, wherein fused thermoplastic resin is extruded from a slit set so as to have a width substantially equal to that of the web and having a plurality of resin supply lines up to the slit branched on the same plane to thereby cover at least one side of the moving bundle of continuous fibers which are opened in a web form.

Description: The present invention relates to an apparatus and a method for producing a long fiber-reinforced thermoplastic resin composition composed of a thermoplastic resin and fiber bundles. The invention also relates to a die used in the production of composite materials of a thermoplastic resin and fiber bundles, and more particularly, to a coating die used in the production of a long fiber-reinforced thermoplastic resin composition. As examples of apparatus for producing long fiber-reinforced thermoplastic resin compositions, there are coating dies with interior passages. Fiber bundles are passed continuously through the interior passages, while a thermoplastic resin melt is extruded into the passages for coating the fiber bundles. The resin coat is allowed to permeate into the fiber bundles. US patent 3551155 discloses a device for forming a compact ribbon of strands of filaments impregnated with synthetic resin. The resin is for example applied to each of the strands individually after they have begun to move through a finite longitudinal distance over which the strands become substantially contiguous to each other. Each of the strands is fed individually into a groove into which resin is also fed. Japanese Patent Application Laid-open (kokai) No. 63-264326 discloses a coating die used in the production of thermoplastic resin profiles reinforced with continuous long fibers. Continuous roving fibers in the form of a web are coated with a thermoplastic resin inside the die. Fig. 3 in the present specification is an example of the die used for coating described in that publication. A thermoplastic resin supplied from an extruder to supply tubes 2 and 2' as indicated by arrows F 1 and F 2 is allowed to pass through slits S 1 and S 2 for permeating into and coating a roving in its width direction W while the roving is moved in the direction of arrow H. The coating die disclosed in Japanese Patent Application Laid-open (kokai) No. 63-264326 has the drawback that supply of a resin melt, coating of fiber bundles, and impregnation of fiber bundles tend to become uneven in the width direction of the roving. Moreover, differences in supply pressure and in amount of supply of the resin which is supplied in the width direction of the roving brings about further problems of clogging of the die and breakage of fibers which occurs due to the uneven shear force against the resin generated inside the subsequent forming die. US patent 5112206 is directed to a pultrusion die for impregnating a fibre with a hardenable resin. Two reactive resin streams are mixed adjacent to fibres being pultruded through the die, the resin streams wetting the fibres. An ultrasonic driver agitates the resins and fibres to accelerate the rate of fibre wetting and to overcome the possibility of uneven distribution of the resin. In one example the resin streams are introduced through two resin distribution networks disposed at an angle to each other and offset relative to each other across the width of the web. The present invention was accomplished after careful studies in view of the above problems. It is therefore an object of the present invention to solve the above problems and to provide coating die apparatus, and a method, for producing a long fiber-reinforced thermoplastic resin composition. Accordingly, the present invention provides a coating die for producing a long fiber-reinforced thermoplastic resin composition in which at least one of the upper and lower sides of a fibrous web which has undergone fiber-loosening and which passes through the die is coated with a thermoplastic resin melt extruded through a slit having substantially the same width as that of the web, characterized in that the die comprises a resin feed path to the slit (43), the said resin feed path having a plurality of resin supply paths (9/12,10/11, 13-16, 17-24 & 25-40) successively and symmetrically branched in the same plane within the die (4). The term "fibrous web" as used herein refers to a web-like continuous bundle of fibers to be passed through the die. According to one aspect of the present invention it is preferable that the total cross-sectional area of successive branch paths across the coating die is equal to or slightly smaller than that of the preceding path or branches (respectively). Another aspect of the present invention is that it is preferable that the lengths of the branched paths to one side of the central axis of the die are equal to the lengths of the corresponding branch paths to the other side of the central axis. The invention also provides a method for producing a long fiber-reinforced thermoplastic resin composition characterized in that at least one side of a fibrous web which has undergone fiber-loosening is coated with a thermoplastic resin melt extruded through a slit having substantially the same width as that of the web, characterized in that the resin is supplied to the slit through a resin feed path having a plurality of resin supply paths successively and symmetrically branched in the same plane within the die. Hereafter, a description will be given to a typical embodiment of a coating die for producing a long fiber-reinforced thermoplastic resin composition in each aspect of the invention. In the coating die for producing long fiber-reinforced thermoplastic resin compositions of the present invention, a resin introduced into a die is extruded through a slit elongated in the width direction of a fibrous web by branching the flow of a resin melt passing through a resin supply path leading to a slit. Therefore, compared to the method in which a resin is introduced to a slit from one supply port via one supply path, the coating die of the invention provides effects of reducing differences in pressure loss and uneven extrusion in the longitudinal direction of the slit, i.e., in the width direction of a web. Moreover, the resin supply path starting with one supply port is branched, in the same plane, into at least two branches in a symmetrical manner with respect to a line passing through the center of the die. The number of branches may be increased as needed. Thus, uneven extrusion, in the width direction of a web, of a resin melt supplied through a slit can be suppressed in accordance with the order of branching. Furthermore, by carving branches in split dies which are in plane symmetry to form branched paths in the die and by assembling the split dies so that the planes of symmetry come together, it is possible to manufacture, with ease, a die of the present invention capable of reducing unevenness of extrusion in the width direction of a web. Brief Description of the Drawings: Fig. 1 is a plan view showing a resin supply path of a coating die for producing a long fiber-reinforced thermoplastic resin composition according to one embodiment of the present invention. Fig. 2 is a side sectional view of the coating die shown in Fig. 1. Fig. 3 is a perspective view showing a conventional coating die according to the prior art disclosed above. Some of essential reference numerals are listed below. 3: Supply port 4: Coating die 5: Path preceding to branches 11, 12: Branched paths 25 through 40: Terminal paths 43: Slit F: Direction of conveying a web An embodiment of the coating die for producing a long fiber-reinforced thermoplastic resin composition according to the present invention will next be described with reference to the drawings. Fig. 1 is a plan view showing the resin supply paths formed in the split dies of the present invention. Fig. 2 shows its side sectional view. In Fig. 1, a thermoplastic resin melt is supplied from an extruder 1 to a supply port 3 of the die. The thermoplastic resin melt introduced into the die 4 is branched to branch paths 9 and 10 which are in a right-and-left symmetry (line, plane) with respect to the central axis M of the die. The total cross-sectional area of the branch paths 9 and 10 is preferably equal to or slightly smaller than that of the path 5. Also, the lengths of the paths 9 and 10 are preferably equal to each other. The branch path 10 turns its direction to the direction in which the web advances. The branch path 11 further branches to equivalent branch paths 13 and 14 which are in a line and plane symmetry with respect to the central axis of the branch path 11. Similarly, the branch path 12 further branches to equivalent branch paths 15 and 16 which are in a line and plane symmetry with respect to the central axis of the branch path 12. Thus, the paths 13 and 14 are branched from the path 11 in a symmetrical manner with respect to the central axis N of the path 11. The paths 15 and 16 are branched from the path 12 in a symmetrical manner with respect to the central axis P of the path 12. In this case, the layouts of the paths 13 and 14 are such that the paths 13 and 16 are in symmetry with respect to the central axis M, and the paths 14 and 15 are in symmetry with respect to the central axis M. The paths 17, 18 branched from the path 13 and terminal paths 25, 26, 27, and 28 branched from the paths 17 and 18 are disposed in symmetry with the paths 19, 20 branched from the path 14 and terminal paths 29, 30, 31, and 32 branched from the paths 19 and 20. Terminal paths 25, 26, 27, 28, 29, 30, 31, and 32 of their entirety are disposed in line in the longitudinal direction of the slit and in symmetry with the terminal paths 33, 34, 35, 36, 37, 38, 39, and 40 with respect to the central axis M. With this structure, the resin flow, which is symmetrical with respect to each axis, is forwarded with pressure to a slit-like accumulation section 41. As a result, the pressurized resin can be conveyed through a slit-like passage 42 shown in Fig. 2 to a slit 43 in a uniform state in the width direction of the web. As described above, the resin melt is conveyed under pressure to the slit-like passage 42 via the slit-like accumulation section 41 after it passes through terminal branch paths 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, and 40 shown in Figs. 1 and 2. When the resin is extruded through the slit 43 to permeate into web-like fiber bundles which are conveyed in the direction as shown by the arrow F in Fig. 2, reduced unevenness in extrusion volume in the direction of the width of the web can be obtained, in other words, extrusion with reduced difference in extrusion pressure of a resin melt can be performed. When a continuous web-like fiber bundle is coated with a thermoplastic resin melt, the resin melt may be extruded from above the web or from both the above and beneath the web as shown in Fig. 3, rather than being extruded from beneath the web. Examples of the thermoplastic resin used for applying to a fibrous web for impregnation include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyamides such as nylon 6, nylon 66, nylon 11, nylon 12, nylon 610 and nylon 612; other thermoplastic resins such as polyacetals, polycarbonates, polyurethanes, polyphenylene sulfides, polyphenylene oxides, polysulfones, polyetherketones, polyetheramides, polyetherimides, and combinations of these. The molecular weight of these resins is not particularly limited so long as they exhibit proper fiber-reinforcing effects when permeated into the fibers. Various additives may be added to the thermoplastic resins in accordance with the end use of the resin composition and conditions under which the resin composition is used. Such additives include anti-oxidants, antistatics, impregnation accelerators, plasticizers, mold releasing agents, fire retardants, fireproofing aids, crystallizing accelerators, colorants, and fillers. As described above, if the coating die for producing a long fiber-reinforced thermoplastic resin composition of the present invention is used, it is possible to uniformly extrude a resin melt toward a web-like fiber bundle passing through the die via a plurality of branched terminal paths disposed in the width direction of a web.

Claims: A coating die (4) for producing a long fiber-reinforced thermoplastic resin composition in which at least one of the upper and lower sides of a fibrous web which has undergone fiber-loosening and which passes through the die is coated with a thermoplastic resin melt extruded through a slit (43) having substantially the same width as that of the web, characterized in that the die comprises a resin feed path to the slit (43), the said resin feed path having a plurality of resin supply paths (9/12,10/11, 13-16, 17-24 & 25-40) successively and symmetrically branched in the same plane within the die (4). A coating die as claimed in claim 1, characterized in that the total cross-sectional area of successive branch paths (9/12,10/11; 13-16; 17-24; & 25-40) across the die (4) is equal to or slightly smaller than that of the preceding path or branches (5; 9/12,10/11; 13-16; & 17-24 respectively). A coating die as claimed in claim 1 or claim 2, characterised in that the lengths of the branched paths (9/12; 13,14; 17-20; & 25-32) to one side of the central axis (M) of the die (4) are equal to the lengths of the corresponding branch paths (10/11; 15,16; 21-24; & 33-40) to the other side of the central axis (M). A method for producing a long fiber-reinforced thermoplastic resin composition characterized in that at least one side of a fibrous web which has undergone fiber-loosening is coated with a thermoplastic resin melt extruded through a slit (43) having substantially the same width as that of the web, characterized in that the resin is supplied to the slit (43) through a resin feed path having a plurality of resin supply paths (9/12,10/11, 13-16, 17-24 & 25-40) successively and symmetrically branched in the same plane within the die (4).

Inventors: AMAIKE TAKESHI, MURAKAMI HARUJI, NITOH TOSHIKATSU, SHIRAI YOSHIMITSU, AMAIKE, TAKESHI, MURAKAMI, HARUJI, NITOH, TOSHIKATSU, SHIRAI, YOSHIMITSU, NITOH, Toshikatsu 12-11, Imaizumi 3-chome
Applicants: POLYPLASTICS CO, POLYPLASTICS CO. LTD.
Application year: 1994
Main classification: B29C70
IPC codes: B29C70, B29K105, B29C47, B29K101, B29B15